The present invention relates to a color photographic imaging process and system and more specifically to a system wherein the resulting contrast of the image is variable.
The contrast and density range of photographic camera film images can and do vary considerably due to differences in:
1. the light modulating properties of objects in the scene being photographed
2. atmospheric conditions which affect the degree of diffusion of direct sunlight and skylight
3. the color quality and distribution of the light illuminating the objects
4. the spatial arrangement of the objects and the resulting pattern of light and shade
5. the properties of the optical components of the camera
6. the response characteristics of the photographic film
7. the chemical development employed for the creation of the photographic image.
In black-and-white photography a negative camera film is normally converted to a positive reflection print image on a paper support. Compensation is made in the printing step for the variations in negative image contrast and density range through the use of one of two types of printing papers. The first type known as graded paper type, consists of several members of the same basic design which differ primarily with respect to the exposure scale, or contrast. The proper matching of film image density range and paper grade, or contrast, yields a final print image which has the necessary and desired range of tones from white to black. Depending on the kind of photographic work, as many as six different paper grades may be required in order to ensure satisfactory final image quality as regards tone reproduction.
The second type of black-and-white paper is known as variable-contrast paper. Such papers are supplied in a single grade of contrast which can be varied, however, through changes in the color quality of the printing light. As a rule variable contrast printing papers have a shorter exposure scale, and a high inherent contrast, when exposed by blue light than when exposed by green light. Intermediate levels of contrast are obtained by appropriate mixtures of blue and green light. The total range of contrast obtainable with variable-contrast papers is somewhat smaller than that provided by a full graded series of papers, but the convenience and the economic benefits of using a single unit variable-contrast material are so great that about 50% of all users in the United States prefer the variable-contrast type of material. In any event, the need for different contrast levels is clearly recognized and served in black-and-white photography.
In color photography the same problem exists, of course, since the same kind of cameras are used for color as for black-and-white picture taking and since the same type of scenes are photographed with color as with black-and-white films under similar lighting conditions. The addition of hue and chroma to the image does reduce the importance of tone-reproduction somewhat in color as compared to black-and-white photography, but good tone rendition still accounts for about 70% of the total quality of color images. However, because color photographic processes are much more complex than black-and-white it has not been practical to supply color printing papers in more than one contrast grade. Some differences in inherent contrast are found between color papers intended primarily for the printing of amateur color film images in photofinishing laboratories and those aimed at the professional market sector, but by large color papers have been single-contrast materials. Consequently, there has been a quality problem with color prints made by a straight printing procedure.